The invention relates generally to fiber quality measurements for cotton classing, more particularly, to conditioning samples of cotton fiber prior to instrument testing and to conditioning in-process cotton for optimal processing in gins or mills.
Cotton standards are supported by the United States Department of Agriculture (USDA) through its Agricultural Marketing Service (AMS). Cotton standards, and the corresponding classing of cotton, are of great importance in determining the market value of a particular bale of cotton, as well as determining suitability of a particular bale of cotton from a gin for subsequent processing at a particular mill in view of the products and processes of that mill. AMS is responsible for preparing and maintaining such cotton standards and does so in its Standards Section located in Memphis, Tenn.
In 1923, the United States and nine European countries entered into the Universal Cotton Standards Agreement. From that time, up until approximately 1965, USDA/AMS cotton classing xe2x80x9cmeasurementsxe2x80x9d based on the Universal Standards were made entirely by humans. The human measurements included xe2x80x9cgrade,xe2x80x9d xe2x80x9cextraneous matterxe2x80x9d (such as bark and grass), xe2x80x9cpreparationxe2x80x9d (which relates to smoothness of the sample) and xe2x80x9cstaple lengthxe2x80x9d (long fiber content). Instrument-based cotton classing was introduced in 1965, beginning with micronaire, followed in 1980 by High Volume Instruments (HVI), which added measurements of length and strength. HVIs currently measure the fiber qualities of Micronaire, Length, Strength, Color and Trash. Some of those fiber quality measurements, notably strength and length are strongly affected by the fiber moisture content. Some proposed additional measurements, notably stickiness, nep content and cleanability, are also strongly affected by moisture content. It follows that it is very important to assure correct moisture content for fiber quality testing. Historically, this has meant allowing 72 hours equilibration time. More recently, rapid conditioning, as described below, can reduce these equilibration times to about 15 minutes. But in many cases, equilibration times of seconds are needed.
Similarly, optimal processing of cotton fiber is strongly affected by moisture content of the material. Gin and mill processing applications demand conditioning times, that is, times to approach equilibria of various processing performance parameters that are seconds, not minutes.
Accordingly, both testing and processing applications require conditioning times that are much shorter than known. Equally or more importantly, the equilibria reached throughout the sample or process materials must be uniform.
Major factors in sample preparation are the precision and accuracies of environmental conditions in which these steps take place. It is also well known that environmental conditions in the testing zones of materials property testing laboratories or instruments can strongly affect test results. This fact is generally important for fiber testing, and particularly critical for cotton, and other natural fibers, and for rayon, and other man-made fibers.
Prior to more recent developments in xe2x80x9crapid conditioning,xe2x80x9d for more than seventy-five years, certain fiber, yarn, or fabric tests have been conducted under so-called xe2x80x9cStandard Laboratory Environmentxe2x80x9d or ASTM conditions of 65% relative humidity and 70xc2x0 F. (21xc2x0 C.) dry bulb temperature. Since what matters most, for good test results, is not conditions in the lab but conditions in the samples (and within the testing zones) at the time of testing, the various ASTM methods for fiber, yarn, or fabric samples further include the requirement that the samples to be tested be stored or xe2x80x9cconditionedxe2x80x9d in the standard environment for 72 hours prior to testing in the standard environment. This storage time presumably allows the samples to xe2x80x9creach equilibrium.xe2x80x9d It is noted that samples so conditioned are passively equilibrating, and that equilibrium usually refers to sample moisture content. Moisture content is the weight of water in the sample as a percentage of the dry weight of the sample. For cotton, equilibrium moisture content MC is about 7.3% at 65% RH, 70xc2x0 F. (21xc2x0 C.).
It should however be noted that moisture content is only one fiber, yarn, or fabric material property measurement whose equilibrium value is of interest. Others include tenacity, length, stickiness and neps, and such fiber properties are much more important for selling, buying and using the fibers than is moisture content. We note that moisture content affects other fiber material properties, and is therefore a very important control variable, but is not as important for marketing or processing purposes.
Whereas equilibration times of 72 hours historically yield consistent test results, such periods are unacceptably long in today""s intensely competitive and information-hungry marketplace. It is therefore critically important that the tests be executed accurately and precisely, that is, with minimal bias or random errors. But testing before equilibria in the tested properties are reached can disastrously (in profit/loss terms) reduce accuracy and precision. (Equilibrium times are different for different materials test parameters.)
Similar and sometimes more severe constraints apply to optimal process controls. Since fiber processing parameters very strongly depend upon the equilibrium fiber qualities, it is important to control said equilibrium values very rapidly, and also very uniformly.
Recognizing the severe conflict between promptly available results versus good (precise and accurate) results, the United States Department of Agriculture Agricultural Marketing Service, Cotton Division, began investigations in the early 1990""s into actively and rapidly conditioning cotton samples. These investigations were remarkably successful and proved that well-conditioned laboratory air could be actively drawn through HVI samples (as opposed to passive or diffusional mass and heat transfer), which active conditioning or xe2x80x9crapid conditioningxe2x80x9d enabled samples to reach moisture content or strength equilibrium in less than about 15 minutes.
Various United States Department of Agriculture papers describe xe2x80x9crapid conditioning.xe2x80x9d Examples are J. L. Knowlton and Roger K. Alldredge, xe2x80x9cExperience with Rapid Conditioning of HVI Samples,xe2x80x9d Beltwide Cotton Conference, San Diego, Calif., January 1994; and Darryl W. Earnest, xe2x80x9cAdvancements in USDA Cotton Classing Facilities,xe2x80x9d Engineered Fiber Conference, Raleigh, N. C., May 1996. xe2x80x9cRapid conditioningxe2x80x9d is now employed in most of the fourteen USDA/AMS cotton classing offices.
In our earlier efforts to extend USDA rapid conditioning results to small instrument classing operations having one to four HVIs (versus twenty to forty), and not having well-conditioned laboratories, it was discovered that simply drawing 65%, 70xc2x0 F. (21xc2x0 C.) air through the samples for 15 minutes yielded unacceptable test results for very dry and wet samples, and that unacceptably long conditioning times were required to achieve good results. It was also found that sample type (i.e., variety) and size and bulk density affected test results and conditioning times.
More recently, and addressing the concerns noted just above, Shofner et al U.S. Pat. No. 6,029,316 discloses methods and a machine for xe2x80x9crapidlyxe2x80x9d conditioning samples of cotton fiber prior to testing. Twenty-four cotton classing samples, each weighing about 0.25 to 0.75 pounds (113 to 340 grams) are placed within a sample tray having a perforated bottom. The machine includes a sensor for measuring sample moisture content, and a controller for determining a sample specific conditioning cycle based on measured moisture content. The determined conditioning cycle is one which causes the samples to be conditioned to an optimum state for testing. Gas flow conditioning apparatus effects the conditioning cycle by driving a conditioned gas flow through the samples. Key features of such forced ventilation flows through the material are flow velocities of about 100 feet/min and sample specific conditioning cycles having variable temperatures F and relative humidities RH.
In the context of that invention, xe2x80x9crapidlyxe2x80x9d means conditioning a sample within about 15 minutes but much more uniformly and, also more generally, as very dry, wet or large samples can be conditioned employing embodiments of the invention.
Embodiments of the invention condition samples of cotton for satisfactory testing (or processing) in a matter of seconds, and do not require conditioned laboratory or processing facility space, as the conditioning is accomplished internally to the testing instrument or processing machine. Key features of the invention are high velocity gas flows through thin mats of material and delivery of moisture and other chemicals in both gaseous and aerosol forms. Important operational features are total moisture concentration (grams of gaseous and aerosolized water per cubic meter of gas, typically air), precisely controlled aerosol particle size distribution, the balance between aerosolized and gaseous water, and the composition and quantities of other chemicals delivered with the water.